U.S. patent number 5,801,885 [Application Number 08/547,871] was granted by the patent office on 1998-09-01 for head mount type image display unit.
This patent grant is currently assigned to Olympus Optical Co., Ltd.. Invention is credited to Takayoshi Togino.
United States Patent |
5,801,885 |
Togino |
September 1, 1998 |
Head mount type image display unit
Abstract
The invention provides an optical system which is well corrected
in terms of both curvature of field and coma at a field angle of
about 120.degree. and a pupil diameter of about 15 mm and may be
applied to both image pickup and ocular systems. Dioptric elements
11 are located the pupil plane side E and/or image plane side I of
a concentric element 12 including two semitransparent surfaces 121
and 122, said two semitransparent surfaces 121 and 122 being
concave on the pupil plane side E and located such that they
transmit light at least once and reflect light at least once.
Inventors: |
Togino; Takayoshi (Koganei,
JP) |
Assignee: |
Olympus Optical Co., Ltd.
(Tokyo, JP)
|
Family
ID: |
17378770 |
Appl.
No.: |
08/547,871 |
Filed: |
October 25, 1995 |
Foreign Application Priority Data
|
|
|
|
|
Oct 26, 1994 [JP] |
|
|
6-262653 |
|
Current U.S.
Class: |
359/630; 359/631;
359/633; 359/638 |
Current CPC
Class: |
G02B
27/0172 (20130101); G02B 5/30 (20130101); G02B
2027/0178 (20130101); G02B 2027/011 (20130101) |
Current International
Class: |
G02B
27/01 (20060101); G02B 5/30 (20060101); G02B
27/00 (20060101); G02B 027/14 () |
Field of
Search: |
;359/630,631,632,633,638,639,640,737,717,729,730,731 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Epps; Georgia Y.
Assistant Examiner: Mack; Ricky
Attorney, Agent or Firm: Cushman Darby & Cushman IP
Group of Pillsbury Madison & Sutro LLP
Claims
What we claim is:
1. A head mount type of image display unit including an image
display unit body having an image display device for displaying an
image and an ocular system for guiding an image displayed on said
image display device to the eyeballs of a viewer, and a support
member mounted over the head of the viewer while it is in contact
therewith, so that said image display unit body is held just before
the face of the viewer, characterized in that:
said ocular system includes, in order from the eye side of the
viewer along the visual axis,
a first prism having a first surface concave on the eye side and a
second surface located on the side of said first prism opposite to
the first surface thereof and concave on the eye side with a medium
having a refractive index (n) larger than 1 (n>1) interposed
therebetween, and
a second prism having a third surface concave on the eye side and
located on the side of said second prism opposite to the eye side
and a medium having a refracti ve index (n) larger than 1
(n>1),
said first prism being designed such that a beam of rays leaving
said image display device is reflected at at least said first
surface and then propagates through the medium of said first prism
in a direction opposite to the eye side, while a beam of rays
reflected at said second surface propagates through the medium of
said first prism and then transmits through said first surface,
wherein said first and said second prisms are cemented
together.
2. A head mount type of image display unit including an image
display unit body having an image display device for displaying an
image and an ocular system for guiding an image displayed on said
image display device to the eyeballs of a viewer, and a support
member mounted over the head of the viewer while it is in contact
therewith, so that said image display unit body is held just before
the face of the viewer, characterized in that:
said ocular system includes, in order from the eye side of the
viewer along the visual axis,
a first prism having a first surface which has a shape concave on
the eye side and has an action on both reflecting and transmitting
a beam of rays, a second surface located on the side of said first
prism opposite to the first surface thereof, which has a shape
concave on the eye side and has an action on both reflecting and
trans mitting a beam of rays and a medium interposed between said
first and second surfaces and having a refractive index (n) larger
than 1 (n>1), and
a second prism having a third surface concave on the eye side and
located on the side of said second prism opposite to the eye side
and a medium having a refractive index (n) larger than 1
(n>1),
wherein said first and second prisms are cemented together.
3. A head mount type of image display unit including an image
display unit body having an image display device for displaying an
image and an ocular system for guiding an image displayed on said
image display device to the eyeballs of a viewer, and a support
member mounted over the head of the viewer while it is in contact
therewith, so that said image display unit body is held just before
the face of the viewer, characterized in that:
said ocular system includes, in order from the eye side of the
viewer along the visual axis,
a first prism having a first surface concave on the eye side and a
second surface located on the side of said first prism opposite to
the first surface thereof and concave on the eye side with a medium
having a refractive index (n) larger than 1 (n>1) interposed
therebetween, and
a second prism having a third surface concave on the eye side and
located on the side of said second prism opposite to the eye side
and a medium having a refractive index (n) larger than 1
(n>1),
said first prism being designed such that a beam of rays leaving
said image display device is reflected at at least said first
surface and then propagates through the medium of said first prism
in a direction opposite to the eye side, while a beam of rays
reflected at said second surface propagates through the medium of
said first prism and then transmits through said first surface,
wherein said prism has a total reflection action, so that a beam of
rays leaving said image display device undergo total reflection at
said first surface and then at said second surface.
4. A head mount type of image display unit including an image
display unit body having an image display device for displaying an
image and an ocular system for guiding an image displayed on said
image display device to the eyeballs of a viewer, and a support
member mounted over the head of the viewer while it is in contact
therewith, so that said image display unit body is held just before
the face of the viewer, characterized in that:
said ocular system includes, in order from the eye side of the
viewer along the visual axis,
a first prism having a first surface which has a shape concave on
the eye side and has an action on both reflecting and transmitting
a beam of rays, a second surface located on the side of said first
prism opposite to the first surface thereof, which has a shape
concave on the eye side and has an action on both reflecting and
transmitting a beam of rays and a medium interposed between said
first and second surfaces and having a refractive index (n) larger
than 1 (n>1), and
a second prism having a third surface concave on the eye side and
located on the side of said second prism opposite to the eye side
and a medium having a refractive index (n) larger than 1
(n>1),
wherein said prism has a total reflection action, so that a beam of
rays leaving said image display device undergo total reflection at
said first surface and then at said second surface.
5. The head mount type of image display unit as recited in claims
1-4, characterized in that the center of curvature of a surface
portion of said first surface intersecting the visual axis and the
center of curvature of a surface portion of said third surface
intersecting the visual axis lie on the same optical axis.
6. The head mount type of image display unit as recited in one of
claims 1-4, characterized in that the radius of curvature of a
surface portion of said first surface intersecting the visual axis
is substantially identical in shape with the radius of curvature of
a surface portion of said third surface intersecting the visual
axis.
7. The head mount type of image display unit as recited in one of
claims 1-4, characterized in that a surface portion of said second
surface intersecting the visual axis is stronger in power (or
smaller in the radius of curvature) than a surface portion of said
third surface intersecting the visual axis.
8. The head mount type of image display unit as recited in one of
claims 1-4, characterized in that a dioptric element having power
is located on the pupil plane side of said first prism, said image
display unit conforming to the following conditions (1 ) and
(2):
where f.sub.1 is the focal length of the dioptric element having
power, R.sub.01 is the radius of curvature thereof on the pupil
plane side, and R.sub.02 is the radius of curvature thereof on the
image surface side.
9. The head mount type of image display unit as recited in one of
claims 1-4, characterized in that a dioptric element having power
is located on the image plane side of said first prism, said image
display unit conforming to the following conditions (3), (4 ) and
(5):
where R.sub.11 is the radius of curvature of the dioptric element
having power on the pupil plane side, R.sub.12 is the radius of
curvature thereof on the image plane side, and R.sub.3 is the
radius of curvature of the semitransparent curved surface of the
first prism located on the image plane side.
10. The head mount type of image display unit as recited in one of
claims 1-4, characterized by conforming to the following condition
(6):
where f.sub.2 is the focal length of the first prism.
11. The head mount type of image display unit as recited in one of
claims 1-4, characterized by conforming to the following condition
(7):
where f.sub.3 is the focal length of the dioptric element having
power, and f.sub.2 is the focal length of the first prism.
12. The head mount type of image display unit as recited in one of
claims 1-4, characterized in that dioptric elements having power
are located on the pupil and image plane sides of said first prism,
said image display unit conforming to the following conditions (8 )
and (9):
where f.sub.1 is the focal length of the dioptric element having
power, which is located on the pupil plane side, f.sub.2 is the
focal length of the first prism, and f.sub.3 is the focal length of
the dioptric element having power, which is located on the image
plane side.
Description
BACKGROUND OF THE INVENTION
The present invention relates generally to an optical system which
can be used as an ocular or image-forming system, and more
particularly to an optical system which is reduced in terms of both
curvature of field and coma and has an improved resolution even at
a wide field angle and a large pupil diameter.
The applicant has already filed Japanese Patent Application No.
5(1993)-264828 for an optical system which enables curvature of
field and coma to be almost completely corrected by filling
vitreous material or the like between at least two semitransparent
curved surfaces to facilitate its production and increasing the
distance between two semitransparent concave surfaces. Even with
the optical system disclosed in the above patent application,
however, curvature of field and coma become noticeable when the
angle of view is as wide as about 100.degree. and the pupil
diameter is as large as about 100 mm.
An account will now be given of why off-axis aberrations are
produced in the optical system disclosed in Japanese Patent
Application No. 5-264828 with reference to an optical path diagram
shown in FIG. 4.
In FIG. 4, reference numeral 1 represents a semitransparent concave
surface located in the vicinity of a pupil plane E and 2 a
semitransparent concave surface located in the vicinity of an image
plane I. A beam of rays is transmitted through or reflected at each
surface in the order of 1-1, 2-1, and 2-2. The beam of rays is
subjected to refraction at 1-1 and 2-2, and to reflection at 1-2
and 2-1.
How to compensate for coma will first be explained. To reduce or
substantially eliminate the occurrence of coma at the image plane
I, it is important to reduce the quantity of coma occurring at 1-1
and 2-1 where a beam of off-axis rays is first incident on the
respective semitransparent surfaces 1 and 2. The optical axis
length from the pupil E to the surface 1 is shorter than that from
the pupil 1 to the surface 2. To reduce the angle of incidence of
the beam of off-axis rays at 1-1 and 2-1 and reduce the difference
in the angle of incidence between an off-axis marginal ray above
the optical axis and an off-axis marginal ray below the optical
axis, thereby reducing the quantity of coma produced, it is
required that the surface 1 be stronger in power than the surface 2
and a curvature difference be between the surfaces 1 and 2.
To reduce the quantity of coma occurring at 1-2 and 2-2 where the
beam of off-axis rays are again incident on the respective
semitransparent surfaces, too, the power of the surface 1 should be
stronger than that of the surface 2. This is because when the power
of the surface 1 is too weak, the angle of inclination of the
normal of the surface 1 becomes small with respect to the optical
axis; so the angle of incidence of an off-axis chief ray at 1-2
becomes large. As a result, there is a large difference in the
angle of incidence between the marginal rays above and below the
optical axis, which otherwise gives rise to some considerable coma.
It is here noted that the image-forming system disclosed is an
almost telecentric one on the image side. When the power of the
surface 2 is too strong, it is located nearly parallel to the
optical axis; so the angle of an off-axis chief ray incident on 2-2
becomes large, resulting in a large difference in the angle of
incidence between the marginal rays above and below the optical
axis and hence giving rise to some considerable coma. To reduce the
quantity of coma occurring at 1-2 and 2-2, it is then required that
the power of the surface 1 be strong and the power of the surface 2
be weak.
Reference will now be made to where curvature of field takes place
primarily and how to compensate for it. The largest curvature of
field is negative curvature of field produced upon reflection at
1-2, and positive curvature of field produced upon reflection at
2-1. To inhibit the occurrence of curvature of field at the image
plane 1, it is required that uniform power be imparted to the
surfaces 1 and 2, so that the negative curvature of field produced
upon reflection at the surface 1 and the positive curvature of
field upon reflection are the surface 2 can be offset each
other.
In the optical system disclosed in Japanese Patent Application No.
5-264828, how to correct coma is in contradiction to how to correct
curvature of field, as already mentioned. In other words, it is
difficult to correct both the aberrations at the same time. If the
field angle and pupil diameter are not particularly large, it is
then possible to correct curvature of field and coma by placing the
powers of both semitransparent concave surfaces 1 and 2 in a well
balanced state. When the field angle and pupil diameter are large,
however, difficulty is involved in preventing curvature of field
and coma from becoming worse.
SUMMARY OF THE INVENTION
In view of the problems associated with the optical system
disclosed in Japanese Patent Application No. 5-264828 filed by the
applicant, the present invention has been accomplished for an
optical system including first and second surfaces 201 and 202 with
the convex surface lying in a direction shown by an arrow 200, as
can be seen from FIG. 22(a). In particular, a concentric system
(element) wherein the center of curvature 201a of a first surface
201 and the center of curvature 202a of a second surfaces 202 are
located side by side on the same optical axis 203, as illustrated
in FIG. 22(b), is desired because more improved aberration
performance is achieved. Then, an object of the present invention
is to provide an optical system which is well corrected in terms of
both curvature of field and coma at a field angle of about
120.degree. and a pupil diameter of about 15 mm and can be used for
both image pickup and ocular systems.
Another object of the present invention is to provide a head mount
type of image display unit which is compact and has a wide field
angle.
To achieve the objects above mentioned, the optical system
according to the present invention is characterized in that at
least one dioptric element is located in the vicinity of a
concentric element including at least two semitransparent surfaces,
said at least two semitransparent surfaces being concave on the
pupil plane side and located such that they transmit light at least
once and reflect light at least once.
In one preferable embodiment of the present invention, it is
desired that a dioptric element having power be located on the
pupil plane side of the concentric element and the following
conditions (1) and (2) be satisfied as well.
Here, f.sub.1 is the focal length of the dioptric element having
power, R.sub.01 is the radius of curvature thereof on the pupil
plane side, and R.sub.02 is the radius of curvature thereof on the
image plane side.
In another preferable embodiment of the present invention, it is
desired that a dioptric element having power be located on the
image plane side of the concentric element and the following
conditions (3), (4) and (5) be satisfied as well.
Here, R.sub.11 is the radius of curvature of the dioptric element
having power on the pupil plane side, R.sub.12 is the radius of
curvature thereof on the image plane side, and R.sub.3 is the
radius of curvature of the semitransparent curved surface of the
concentric element located on the image plane side.
One head mount type of image display unit according to the present
invention includes an image display unit body having an image
display device for displaying an image and an ocular system for
guiding an image displayed on said image display device to the
eyeballs of a viewer, and a support member mounted over the head of
the viewer while it is in contact therewith, so that said image
display unit body is held just before the face of the viewer,
characterized in that:
said ocular system includes, in order from the eye side of the
viewer along the visual axis,
a first prism having a first surface concave on the eye side and a
second surface concave on the eye side with a medium having a
refractive index (n) larger than 1 (n>1) interposed
therebetween, and
a second prism having a third surface concave on the eye side and
located on the side opposite to the eye side and a medium having a
refractive index (n) larger than 1 (n>1),
said first prism being designed such that a beam of rays leaving
said image display device is reflected at at least said first
surface and then propagates through the medium of said first prism
in a direction opposite to the eye side, while a beam of rays
reflected at said second surface propagates through the medium of
said first prism and then transmits through said first surface.
Another head mount type of image display unit according to the
present invention includes an image display unit body having an
image display device for displaying an image and an ocular system
for guiding an image displayed on said image display device to the
eyeballs of a viewer, and a support member mounted over the head of
the viewer while it is in contact therewith, so that said image
display unit body is held just before the face of the viewer,
characterized in that:
said ocular system includes, in order from the eye side of the
viewer along the visual axis,
a first prism having a first surface which has a shape concave on
the eye side and has an action on both reflecting and transmitting
a beam of rays, a second surface which has a shape concave on the
eye side and has an action on both reflecting and transmitting a
beam of rays and a medium interposed between said first and second
surfaces and having a refractive index (n) larger than 1 (n>1),
and
a second prism having a third surface concave on the eye side and
located on the side opposite to the eye side and a medium having a
refractive index (n) larger than 1 (n>1).
Reference will now be made to why the above-mentioned arrangements
are adopted and how they work. The optical system of the present
invention will now be explained chiefly with reference to an
image-forming system for simplicity of illustration. As will be
obvious to those skilled in the art, however, the optical system of
the present invention may be used as an ocular system with an
object point defined by an image plane; in other words, the optical
system of the present invention may function as an ocular system,
if the construction of the image-forming system is reversed. With
regard to the signs of curvature of field and coma, the present
invention will also be explained following the definition set forth
in Y. Hayami, "Optics I for Optical Equipment" (the
Optomechatronics Association).
The reason why the occurrence of various aberrations is reduced in
an optical system having such curvature that the convex surface
lies in a substantially identical direction, especially in a
concentric system (element) is mentioned in Japanese Patent
Application No. 5-264828. However, this optical system has reduced
aberrations but, instead, is low in terms of the degree of freedom
of power distribution. For instance, when there are some
limitations such as a limitation to total lens length with respect
to focal length, the relation between the radii of curvature of two
semitransparent surfaces becomes ill-balanced, so making it
difficult to make satisfactory correction for curvature of field.
According to the present invention, an optical system having
reduced curvature of field is achieved by adding a dioptric
element(s) to the concentric system (element), thereby correcting a
Petzval's sum.
A specific arrangement wherein the dioptric element is located on
the pupil plane side of the concentric element will first be
explained with reference to FIG. 1.
FIG. 1 is an optical path diagram of the arrangement wherein the
dioptric element having power is located in contact with the pupil
plane side of the concentric element. Reference numeral 11
represents a dioptric element having power, 12 a concentric element
constructed from two semitransparent curved surfaces concave on a
pupil plane side E, 111 a refracting surface of the dioptric
element 11 having power, which is located on the pupil plane side
E, 121 the semitransparent curved surface of the concentric element
12 located on the pupil plane side E, and 122 the semitransparent
curved surface of the concentric element 12 located on an image
plane side I.
With an arrangement consisting of the concentric element 12 alone,
difficulty is involved in correcting curvature of field and coma
when the angle of view exceeds 90.degree.. If the angle of view is
about 60.degree., however, it is then possible to make sufficient
correction for both the aberrations. To make the angle of view
wide, therefore, is achieved by use of the dioptric element which
serves to refract a beam of off-axis rays toward the pupil plane
side E of the concentric element 12 with positive power, thereby
reducing the field angle of the beam of off-axis rays incident on
the concentric element 12. Then, it is important to take care of
the shape of the dioptric element 11 having positive power; that
is, it is important to use the dioptric element 11 in the form of a
plano-convex lens, thereby minimizing an adverse influence on the
concentric element 12. This is because by allowing the surface 111
to have a shape close to a planar shape, a beam of off-axis rays
are largely reflected at the surface 111 so that the field angle of
the off-axis rays incident on the concentric element 12 can be
reduced, irrespective of the fact that the surface 111 is almost
unlikely to yield curvature of field and coma. By placing the
indices of refraction of the vitreous materials forming the
dioptric and concentric elements 11 and 12 in a well balanced
state, the curvature of field produced upon refraction at the
surface 121 can be made either positive or negative; so the
quantity of the curvature of field produced can be readily
controlled. Thus, the curvature of field produced upon reflection
at the surfaces 121 and 122 and upon refraction at the surface 122
can be easily corrected at the surface 121.
More exactly, it is important that the arrangement wherein the
dioptric element 11 having power is located on the pupil plane side
of the concentric element 12 conform to the following conditions
(1) and (2):
Here, f.sub.1 is the focal length of the dioptric element 11,
R.sub.01 is the radius of curvature thereof on the pupil plane side
E, and R.sub.02 is the radius of curvature thereof on the image
plane side I.
In FIG. 1, the dioptric element 11 is shown to be cemented to the
concentric element 12. Even when the dioptric element 11 is spaced
away from the concentric element 12, however, it is again important
that the above-mentioned conditions (1) and (2) are satisfied. When
there is air between the dioptric element 11 and the concentric
element 12, curvatures of field of opposite signs are produced upon
refraction at the refracting surface of the dioptric element 11
located on the image plane side I and the surface 121. By placing
these two surfaces in a well-balanced state, therefore, positive or
negative curvature of field can be freely produced by the time a
beam of off-axis rays is incident from the refracting surface of
the dioptric element 11 located on the image plane side I on the
surface 121. In other words, even when the dioptric element 11
comes in no cemented contact with the concentric element 12, the
same actions as above mentioned can be achieved by conforming to
the above-mentioned conditions (1) and (2).
Another specific arrangement wherein the dioptric element is
located on the image plane side of the concentric element made up
of two semitransparent curved surfaces concave on the pupil plane
side E will then be explained with reference to FIG. 2.
FIG. 2 is an optical path diagram of the arrangement wherein a
dioptric element having power is spaced away from the image plane
side of a concentric element constructed from two semitransparent
curved surfaces concave on the pupil plane side. Reference numeral
13 represents a dioptric element having power, 12 a concentric
element, 131 a refracting surface of the dioptric element 13
located on the pupil plane side E, 132 a refracting surface of the
dioptric element 13 located on the image plane side I, 121 the
semitransparent curved surface of the concentric element 12 located
on the pupil plane side E, and 122 the semitransparent curved
surface of the concentric element 12 located in the image plane
side I.
This arrangement is likely to yield off-axis aberrations such as
curvature of field and coma in the concentric element 12, because
the field angle of a beam of off-axis rays incident on the
concentric element 12 remains large. As already explained with
reference to the prior art, how to correct curvature of field is in
contradiction to how to correct coma. When the field angle of a
beam of off-axis rays incident on the concentric element 12 is
large, the powers of the surfaces 211 and 122 are likely to become
ill-balanced. In particular, the surface 122 must have some strong
power so as to correct curvature of field. A telecentric
arrangement on the image side, for instance, this arrangement, is
likely to yield excessive coma when a beam of off-axis rays
undergoes refraction at the surface 122, because the angle of an
off-axis chief ray incident on the surface 122 with respect to the
optical axis is small. Due to correction for coma, the powers of
the surfaces 121 and 122 become ill-balanced, thus causing
curvature of field to remain.
To avoid this, the off-axis aberrations remaining in the concentric
element 12 are compensated for by the provision of the dioptric
element 13 on the image plane side I of the concentric element 12.
It is then required that the curvature of field and coma produced
at the concentric element 12 be concurrently compensated for in
view of the shape of the dioptric element 13; so it is important
that the dioptric element 13 is made up of a meniscus lens concave
on the pupil plane side E. By use of the dioptric element 13 in the
form of a meniscus lens, curvatures of field of opposite signs are
produced at the front and rear surfaces 131 and 132 of the lens. By
a suitable choice of the balance of power between the surfaces 131
and 132, the dioptric element 13 can produce positive or negative
curvature of field, so that the curvature of field remaining in the
concentric element 12 can vanish readily.
For correction of coma, it is important that the power of the
refracting surface 132 of the meniscus lens 13 located on the image
plane side I is weaker than that of the surface 122. By allowing
the surface 122 to have power, it is prima facie possible to reduce
the quantity of coma produced upon reflection at the surface 122.
However, much coma occurs because the power of the surface 122
becomes too strong upon refraction at the surface 122. Such coma at
the image plane I can be reduced if the surfaces 122 and 132 play
different roles, viz., if the surface 122 plays a main role in
reducing the quantity of coma produced upon the reflection of a
beam of off-axis rays and if the surface 132 plays a main role in
reducing the quantity of coma produced upon the refraction of a
beam of off-axis rays. In short, a part of the large coma produced
at the surface 122 is offset by the surface 131 by making the power
of the surface 132 weaker than that of the surface 122, thus making
it possible to produce the quantity of coma needed for offsetting
the coma produced at the concentric element 12 by the surface
132.
More exactly, it is important to satisfy the following conditions
(3), (4) and (5):
Here, R.sub.11 is the radius of curvature of the pupil-side
refracting surface 131 of the dioptric element 13 having power,
located on the image plane side I, R.sub.12 is the radius of
curvature of the refracting surface 132 thereof on the image plane
side I, and R.sub.3 is the radius of curvature of the
semitransparent curved surface of the concentric element 12 located
on the image plane side I. In the ocular system, the conditions (3)
and (4) are respectively rewritten as
The power of the meniscus lens 13 is either positive or negative
depending on the powers of the front and rear refracting surfaces
131 and 132 thereof. Since aberrations of opposite signs are
produced at the front and rear refracting surfaces of 131 and 132
of the meniscus lens 13, however, it is required that the front and
rear refracting surfaces 131 and 132 of the meniscus lens 13 have
different powers so as to make correction for aberrations produced
at the two semitransparent curved surfaces 121 and 122; so the
power of the meniscus lens 13 is in no sense zero.
In the arrangement shown in FIG. 2, the dioptric element 13 is in
no cemented contact with the concentric element 12. Even when the
dioptric element 13 and optical system 12 are in cemented contact
with each other, however, it is important to conform to the
above-mentioned conditions (4) and (5). When the dioptric and
concentric elements 13 and 12 are brought into cemented contact
with each other, the surface 122 has power enough to inhibit coma
upon reflection thereat while the surface 132 has power enough to
inhibit coma upon refraction thereat, because off-axis aberrations
hardly occur upon refraction at the surface 121. In other words,
even when the dioptric element 13 comes into cemented contact with
the concentric element 12, the same actions as above mentioned are
achievable by conforming to the above-mentioned conditions (4) and
(5).
It is noted that when the concentric element 12 with the dioptric
element 13 of power located on the image plane side I is used as
the ocular system of a head mount type of image display unit, the
radius of curvature R.sub.12 of the refracting surface 132 of the
dioptric element 13 located on the image plane side I should
preferably be such that the curved surface is concave on the pupil
plane side E, as is the case with the radius of curvature of the
semitransparent curved surface 121 located on the pupil plane side
E of the concentric element 12. For the head mount type of image
display unit that needs an extra space, is heavy and is to be
mounted over the head, it is very desired that the refracting
surface 132 of the dioptric element 13 located on the image plane
side I is either a planar surface or a curved surface concave on
the image plane side I.
More preferably, and to obtain an image of higher resolution, the
following condition should be satisfied.
For the arrangement wherein the dioptric element 11 having power is
located on the pupil plane side E of the concentric element 12 made
up of two semitransparent curved surfaces concave on the pupil
plane side E, it is important to conform to the following condition
(6):
Here f.sub.1 is the focal length of the dioptric element 11 having
power and f.sub.2 is the focal length of the concentric element
12.
When the value of the above condition (6) exceeds the upper limit
of 0.42, negative curvature of field produced at the concentric
element 12 is undercorrected by the dioptric element 11; so the
negative curvature of field becomes noticeable on the image plane
I. When the value of the above condition (6) is below the lower
limit of 0, on the contrary, positive curvature of field produced
at the concentric element 12 is undercorrected by the dioptric
element 11; so the positive curvature of field becomes noticeable
on the image plane I.
For the arrangement wherein the dioptric element 13 having power is
located on the image plane side I of the concentric element 12 made
up of two semitransparent curved surfaces concave on the pupil
plane E, it is important to conform to the following condition
(7):
Here f.sub.3 is the focal length of the dioptric element 13 having
power, which is located on the image plane side I, and f.sub.2 is
the focal length of the concentric element 12.
When the value of the above condition (7) exceeds the upper limit
of 0.2, negative curvature of field produced at the concentric
element 12 is undercorrected by the dioptric element 13; so the
negative curvature of field becomes noticeable on the image plane
I. When the value of the above condition (7) is below the lower
limit of -0.4, on the contrary, positive curvature of field
produced at the concentric element 12 is undercorrected by the
dioptric element 13; so the positive curvature of field becomes
noticeable on the image plane I.
More preferably, and to obtain an image of higher resolution at a
wider field angle, it is desired that dioptric elements conforming
to the following conditions (8) and (9) be located on both the
pupil position and image plane side of the optical system.
More preferably, and to obtain an image of higher resolution at a
wider field angle, it is desired that dioptric elements conforming
to the following conditions (8) and (9) be located both the pupil
and image plane sides of the concentric element.
When a dioptric element having power is located on the pupil plane
side, there is a fear that the field angle of a beam of off-axis
rays incident on the concentric element made up of semitransparent
curved surfaces becomes large at a field angle larger than
120.degree.. This is true of even when the field angle of the beam
of off-axis rays is reduced with the positive power of the dioptric
element. When a dioptric element having power is located on the
image plane side, too, there is a fear that if the field angle of a
beam of incident off-axis rays is very large, it is then difficult
to obtain an image of high resolution by offsetting off-axis
aberrations produced at the concentric element by the dioptric
element.
To achieve an optical system having a wider field angle while
off-axis aberrations are well corrected, it is therefore desired
that dioptric elements 11 and 13 having power be located on both
pupil and image plane sides E and I of a concentric element 12, as
shown in FIG. 3. Here, reference numeral 111 represents the
pupil-side refracting surface of the dioptric element 11 located on
the pupil plane side E, 121 the semitransparent curved surface of
the concentric element 12 located on the pupil plane side E, 122
the semitransparent curved surface of the concentric element 12
located on the image plane side I, and 132 the image-side
refracting surface of the dioptric element 13 located on the image
plane side I.
In the arrangement wherein the dioptric elements 11 and 13 are
located on the pupil and image plane sides E and I of the
concentric element 12, aberrations hardly occur upon a beam of
off-axis rays passing through the surfaces 121 and 122 of cemented
contact of the dioptric elements 11 and 13 with the concentric
element 12, if there is a little difference in the index of
refraction between the vitreous materials forming the dioptric
elements 11 and 13 and the concentric element 12. In other words,
it is only upon refraction at the surfaces 121 and 122 where
aberrations are chiefly produced at the concentric element 12. By
placing the powers of the two semitransparent curved surfaces 121
and 122 in a well-balanced state, off-axis aberrations can be
corrected by the concentric element 12 alone, because curvature of
field and coma produced upon refraction at the surfaces 121 and 122
are offset each other.
It is then important to balance the powers of dioptric elements 11
and 13 against that of the concentric element 12. In other words,
it is important to conform to the following conditions (8) and
(9):
Here, f.sub.1 is the focal length of the dioptric element 11 having
power, which is located on the pupil plane side E, f.sub.3 is the
focal length of the dioptric element 13 having power, which is
located on the image plane side I, and f.sub.2 is the focal length
of the concentric element 12.
When the values of the above conditions (8) and (9) exceed the
respective upper limits of 1.0 and 0, negative curvature of field
produced at the concentric element 12 made up of the two
semitransparent curved surfaces 121 and 122 is undercorrected by
the dioptric elements 11 and 13; so the negative curvature of field
becomes noticeable on the image plane I. When the values of the
above conditions (8 ) and (9) are below the respective lower limits
of 0 and -1.2, on the contrary, positive curvature of field
produced at the concentric element 12 is undercorrected by the
dioptric elements 11 and 13; so the positive curvature of field
becomes noticeable on the image plane I.
As above mentioned, the dioptric elements 11 and 13 play a role in
enabling aberrations to be corrected by the concentric element 12
alone. To achieve this, it is more important to prevent the
occurrence of off-axis aberrations upon a beam of off-axis rays
entering the dioptric element 11 and upon a beam of off-axis rays
leaving the dioptric element 13. To this end, it is required to
take the shape of the located dioptric elements 11 and 13 into
consideration. In other words, it is important for the dioptric
element 11 located on the pupil plane side E to have a shape close
to a plano-convex shape, and for the dioptric element 13 located on
the image plane side I to have a shape close to a concavo-planar
shape. By allowing the surface 111 to have a shape close to a
planar shape, the field angle of a beam of off-axis rays can be
extremely reduced with no substantial occurrence of off-axis
aberrations at the surface 111. By allowing the surface 132 to have
a shape close to a planar shape, it is possible to extremely reduce
the angle of incidence of an off-axis chief ray on the surface 132,
said chief ray propagating nearly along the optical axis to the
image plane I, so that the occurrence of off-axis aberrations at
the surface 132 can be substantially eliminated.
Even when the dioptric elements 11 and 13 are brought in no
cemented contact with the concentric element 12, the actions as
above mentioned are again achievable, if the radii of curvature of
the surfaces of the dioptric elements 11 and 13 to face the
concentric element 12 are almost identical with those of the
surfaces 121 and 122 with reduced air separations between the
dioptric elements 11, 13 and the concentric element 12. The reason
is that off-axis aberrations are offset each other by the
image-side surface of the dioptric element 11 and the surface 121,
and the pupil-side surface of the dioptric element 13 and the
surface 122.
It is noted that the transmission-to-reflection ratio of the
semitransparent surfaces used herein may lie in the range of 2:8 to
8:2.
Such division of the quantity of light may be achieved by dividing
the quantity of light in terms of area (area division method)
and/or dividing the intensity of light (intensity division method),
or dividing the quantity of light depending on the angle of
incidence (the critical angle for total reflection).
The above area division method will now be explained with reference
to FIG. 5. As illustrated in FIG. 5, an aluminum coating 42 is
provided on a transparent substrate 41 formed of glass, plastics or
the like. This aluminum coating 42 is provided in a mesh form of a
few .mu.m to about 0.1 mm, so that the overall (macroscopic)
reflectance and transmittance can be determined by the ratio
between an area which reflects light and an area which does not
reflect but transmits light.
One means or method for dividing the quantity of light into the
quantity of transmitted light and the quantity of reflected light
will then be explained with reference to FIG. 6. This means is
achievable relatively easily as well as inexpensively. As
illustrated in FIG. 6, a semitransparent thin film 43 is coated on
a transparent substrate 41 formed of glass, plastics or the like
for the purpose of dividing the quantity of light. Generally, thin
films of metals such as Al (aluminum), and Cr (chromium) may be
used for the semitransparent thin film 43. Alternatively, laminated
thin films of SiO.sub.2, MgF.sub.2, etc., may be used in the form
of a dielectric multilayer film.
Another means or method for making use of polarization to divide
the quantity of light into the quantity of transmitted light and
the quantity of reflected light will now be explained with
reference to FIG. 7. As illustrated in FIG. 7, a polarizing
semitransparent thin film 44 is coated on a transparent substrate
41 formed of glass, plastics or the like for selective transmission
or reflection of p polarized light and S polarized light in a
divided manner, so that reflectance and transmittance can be
determined by the ratio of P polarized light and S polarized light
in the incident light.
The above-mentioned methods may be used in combination with one
another, if desired.
Use may also be made of means for dividing the quantity of light
into the quantity of transmitted light and the quantity of
reflected light by a holographic element.
As an alternative to the above-mentioned easy-to-perform method
comprising the coating of a thin film, use may be made of a method
for dividing the incident light into reflected light and
transmitted light by the angle of incidence of light (the critical
angle for total reflection). According to this method typically
illustrated in FIG. 8(a), light from the image plane I of a liquid
crystal display element (LCD) undergoes total reflection at a first
surface 121 of an ocular system 12 and reflection at a second
surface 122 (which may be either a mirror or a semitransparent
surface), and strikes again on the first surface 121. In this case,
any decrease in the quantity of light occurring at the first
surface 121 can be prevented in the process of guiding a
transmitted image to the eye E of a viewer. A problem associated
with the above-mentioned light division means using thin films,
etc., is that the quantity of light decreases whenever it is
divided. In contrast, the use of total reflection enables rays
S.sub.1 and S.sub.2 whose angles of incidence are larger than the
critical angle for total reflection (.theta.) to undergo total
reflection at the first surface 121 and a ray T whose angle of
incidence is smaller than the critical angle of total reflection
(.theta.) to transmit through the first surface 121, as can be seen
from FIG. 8(b). It is then desired that the first and second
surfaces 121 and 122 be such that the first angle of incidence of
light on the first surface 121 of FIG. 8(a) becomes larger than the
critical angle for total reflection (.theta.) and the second angle
of incidence of light on the first surface 121 after reflection at
the second surface 122 becomes smaller than the critical angle for
total reflection (.theta.), thereby reducing quantitative
losses.
To cut off flare light transmitted through the first and second
surfaces 121 and 122 of the concentric element 12 directly to the
image plane I without reflection at those surfaces whatsoever, it
is important that polarizing elements making use of polarized light
as disclosed in Reissued U.S. Pat. No. 27356 are located. For
instance, a first polarizing plate and a quarter-wave plate are
located on the pupil plane side E of the first surface 121 to
convert the incident light into circularly polarized light. Then,
another quarter-wave plate is located between the first surface 121
and the semitransparent surface of the second surface 122, and a
second polarizing plate with the polarizing surface having a
parallel Nicols relation to the first polarizing plate is located
after the semitransparent surface of the second surface 122. In the
arrangement including such polarizing elements, a normal ray
undergoing reflection at the first and second surfaces 121 and 122
once for each passes three times through the quarter-wave plate
located between the first and second surfaces 121 and 122; so the
normal ray passes four times in all through the quarter-wave plate.
Accordingly, the plane of polarization of the light passing through
the first polarizing plate does not rotate, and passes through the
second polarizing plate having a parallel Nicols relation to the
first polarizing plate. However, the ray passing through the
semitransparent surface of the first surface 121 without undergoing
reflection thereat passes merely through the quarter-wave plate
twice in all, so that it can be cut off by the second polarizing
plate with the plane of polarization rotated through
90.degree..
By use of the polarizing elements, it is thus possible to cut off
flare light. The above arrangement is referred to for the purpose
of illustration alone; so other arrangements of polarizing elements
may be used.
If two sets of such optical systems are used in the form of an
ocular system, it is then unnecessary for a viewer to view an image
with one eye closed. For a viewer, it is possible to view an image
with both eyes in a comfortable manner. By presenting a parallactic
image to both eyes, it is also possible to view the image in the
form of a stereo-graphic image. Moreover, the use of two sets of
the optical systems according to the present invention together
with a support mechanism for supporting them on the head of a
viewer enables an image to be viewed in a comfortable position.
A portable type of visual display unit, for instance, a fixed or
head mount type of image display unit that enables an image to be
viewed with both eyes may be constructed by providing a pair of
visual display sets, each comprising an ocular system defined by
the optical system according to the present invention and a
two-dimensional image display device, and supporting the visual
display sets while they are spaced away from each other by an
eye-to-eye distance. One general construction of such a portable
type of image display unit is shown in FIG. 9. A display unit body
50 includes a pair of ocular systems, each made up of such an
optical system as above mentioned. Associated with these systems, a
two-dimensional image display unit made up of liquid crystal
display devices is located on the image plane, although not
illustrated. Continuously extending from both sides of the body 50
are temple frames 51, as shown, which are in turn joined to each
other by means of a parietal frame 52. Both temple frames 51
include rear frames 54 connected thereto through leaf springs 53,
which are engaged with the rear portions of the ears of a viewer,
like the bows of spectacles, while the parietal frame 52 is placed
over the parietal of the viewer, so that the body 50 can be held
just before the viewer's eyes. Since a parietal pad 55 formed of an
elastomer such as a sponge is provided to the inside of the
parietal frame 52 and similar pads are provided to the insides of
the rear frames 54, this display unit can be mounted over the
viewer's head in a comfortable manner.
Speakers 56 additionally provided to the rear frames 54 enable the
viewer to listen to stereophonic sound while viewing images. As
illustrated, a playback device 58 such as a portable video camera
is connected through an image/sound transmitting cord 57 to the
display unit body 50 including speakers 56. Thus, if the playback
device 58 is held at any desired position of a belt or the like, as
shown, the viewer will then be able to enjoy images and sound at
the same time. In FIG. 9, reference numeral 59 represents a control
panel for a switch of the playback device 58, volume, etc. It is
here noted that electronic parts such as image and sound processing
circuits are built in the parietal frame 52.
The cord 57, if it has a jack at its distal end, may be connected
to an existing video deck, etc. If the cord 57 is connected to a
tuner for receiving TV electric waves, the viewer will then be able
to watch television. If the cord 57 is connected to a computer, the
viewer will then be able to look at computer graphics images or
message images from the computer. For removal of needless cord
portions, external signals may be received by electric waves via an
antenna.
Still other objects and advantages of the invention will in part be
obvious and will in part be apparent from the specification.
The invention accordingly comprises the features of construction,
combinations of elements, and arrangement of parts which will be
exemplified in the construction hereinafter set forth, and the
scope of the invention will be indicated in the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an optical path diagram showing an optical system of the
present invention wherein a dioptric element is cemented to the
pupil side of an optical element having such curvature that the
convex surface lies in a substantially identical direction.
FIG. 2 is an optical path diagram showing an optical system of the
present invention wherein a dioptric element is located on the
image plane side of an optical element having such curvature that
the convex surface lies in a substantially identical direction.
FIG. 3 is an optical path diagram showing an optical system of the
present invention wherein dioptric elements are located on both
sides of an optical element having such curvature that the convex
surface lies in a substantially identical direction.
FIG. 4 is an optical path diagram for illustrating why off-axis
aberrations occur in the prior optical system having such curvature
that the convex surface lies in a substantially identical
direction.
FIG. 5 is a schematic illustrating the principle of means which is
applicable to a semitransparent surface to divide the quantity of
light in terms of area.
FIG. 6 is a schematic illustrating the principle of means which is
applicable to a semitransparent surface to divide the quantity of
light quantitatively.
FIG. 7 is a schematic illustrating the principle of means which is
applicable to a semitransparent surface to divide the quantity of
light by polarization.
FIGS. 8(a) and 8(b) are schematics illustrating means for dividing
the quantity of light into the quantity of reflected light and the
quantity of transmitted by the angle of incidence of light.
FIG. 9 a view showing the general construction of one embodiment of
a portable type of visual display unit.
FIG. 10 is a sectional view of the optical system according to
Example 1 of the present invention.
FIG. 11 is a sectional view of the optical system according to
Example 2 of the present invention.
FIG. 12 is a sectional view of the optical system according to
Example 3 of the present invention.
FIG. 13 is a sectional view of the optical system according to
Example 4 of the present invention.
FIG. 14 is a sectional view of the optical system according to
Example 5 of the present invention.
FIG. 15 is a sectional view of the optical system according to
Example 6 of the present invention.
FIG. 16 is a sectional view of the optical system according to
Example 7 of the present invention.
FIG. 17 is a sectional view of the optical system according to
Example 8 of the present invention.
FIG. 18 is a sectional view of the optical system according to
Example 9 of the present invention.
FIG. 19 is a perspective view for illustrating an embodiment of
application of the optical system according to the present
invention to an image-forming system of the finder system of a
compact camera.
FIG. 20 is a sectional view for illustrating an embodiment wherein
the optical system according to the present invention is used as
part of an objective.
FIGS. 21(a), 21(b) and 21(c) are views for illustrating embodiments
wherein an optical system according to the present invention is
used as an ocular system of a head mount type of visual display
unit.
FIGS. 22(a) and 22(b) are views for illustrating optical systems to
which the present invention is directed.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Reference will now be made to Examples 1-9 of the optical system
according to the present invention.
FIGS. 10 to 18 are sectional views of Examples 1 to 9 of the
optical system according to the present invention. Numerical data
about each example will be given later. In FIGS. 10 to 18, letters
E and I represent the pupil position and the image plane,
respectively, and reference numeral 12 represents a concentric
element made up of a first semitransparent surface 121 and a second
semitransparent surface 122, 11 a dioptric element having power,
which is located on the pupil plane side of the concentric element
12, and 13 a dioptric element having power, which is located on the
image plane side of the concentric element 12.
In Example 1, the first and second semitransparent surfaces 121 and
122 are concave surfaces convex on the image plane side I and a
positive meniscus lens 11 convex on the image plane side I is
cemented to the pupil plane side E of the concentric element 12, as
shown in FIG. 10. In this example, the field angle, pupil diameter,
focal length and F-number are 40.degree., 15 mm, 40 mm and 2.7,
respectively. The value of f.sub.2 /f.sub.1 in Cond. (6) is
0.208.
It is here noted that in the numerical data given later, the
surfaces are numbered in the order that rays pass through them, nd
is the d-line refractive index of a transparent body, and .nu.d is
the Abbe's number thereof.
In Example 2, the first and second semitransparent surfaces 121 and
122 are concave surfaces convex on the image plane side I and a
positive meniscus lens 11 convex on the image plane side I is
cemented to the pupil plane side E of the concentric element 12, as
shown in FIG. 11. In this example, the field angle, pupil diameter,
focal length and F-number are 120.degree., 6 mm, 40 mm and 6.7,
respectively. The value of f.sub.2 /f.sub.1 in Cond. (6) is
0.039.
In Example 3, the first and second semitransparent surfaces 121 and
122 are concave surfaces convex on the image plane side I and a
positive meniscus lens 11 convex on the image plane side I is
cemented to the pupil plane side E of the concentric element 12, as
shown in FIG. 12. In this example, the field angle, pupil diameter,
focal length and F-number are 120.degree., 15 mm, 40 mm and 2.7,
respectively. The value of f.sub.2 /f.sub.1 in Cond. (6) is
0.146.
In Example 4, the first and second semitransparent surfaces 121 and
122 are concave surfaces convex on the image plane side I and a
positive meniscus lens 11 convex on the image plane side I is
spaced away from the pupil plane side E of the concentric element
12, as shown in FIG. 13. In this example, the field angle, pupil
diameter, focal length and F-number are 120.degree., 15 mm, 40 mm
and 2.7, respectively. The value of f.sub.2 /f.sub.1 in Cond. (6)
is 0.082.
In Example 5, the first and second semitransparent surfaces 121 and
122 are concave surfaces convex on the image plane side I and a
negative meniscus lens 13 convex on the image plane side I is
cemented to the image plane side I of the concentric element 12, as
shown in FIG. 14. In this example, the field angle, pupil diameter,
focal length and F-number are 120.degree., 10 mm, 40 mm and 4.0,
respectively. The value of f.sub.2 /f.sub.3 in Cond. (7) is
-0.031.
In Example 6, the first and second semitransparent surfaces 121 and
122 are concave surfaces convex on the image plane side I and a
positive meniscus lens 13 convex on the image plane side I is
spaced away from the image plane side I of the concentric element
12, as shown in FIG. 15. In this example, the field angle, pupil
diameter, focal length and F-number are 90.degree., 6 mm, 40 mm and
6.7, respectively. The value of f.sub.2 /f.sub.3 in Cond. (7) is
0.037.
In Example 7, the first and second semitransparent surfaces 121 and
122 are concave surfaces convex on the image plane side I, and a
double-convex lens 11 is cemented to the pupil plane side E of the
concentric optical element 12 while a negative meniscus lens 13
convex on the image plane side I is cemented to the image plane
side I of the concentric element 12, as shown in FIG. 16. In this
example, the field angle, pupil diameter, focal length and F-number
are 120.degree., 10 mm, 40 mm and 4.0, respectively. The value of
f.sub.2 /f.sub.1 in Cond. (8) is 0.440, and the value of f.sub.2
/f.sub.3 in Cond. (9) is -0.577.
In Example 8, the first and second semitransparent surfaces 121 and
122 are concave surfaces convex on the image plane side I, and a
double-convex lens 11 is cemented to the pupil side E of the
concentric element 12 while a negative meniscus lens 13 convex on
the image plane side I is cemented to the image plane side I of the
concentric element 12, as shown in FIG. 17. In this example, the
field angle, pupil diameter, focal length and F-number are
40.degree., 15 mm, 40 mm and 2.7, respectively. The value of
f.sub.2 /f.sub.1 in Cond. (8) is 0.174, and the value of f.sub.2
/f.sub.3 in Cond. (9) is -0.029.
In Example 9, the first and second semitransparent surfaces 121 and
122 are concave surfaces convex on the image plane side I, and a
double-convex lens 11 is spaced slightly away from the pupil plane
side E of the concentric element 12 while a negative meniscus lens
13 convex on the image plane side I is spaced slightly away from
the image plane side I of the concentric element 12, as shown in
FIG. 18. In this example, the field angle, pupil diameter, focal
length and F-number are 90.degree., 10 mm, 40 mm and 4.0,
respectively. The value of f.sub.2 /f.sub.1 in Cond. (8) is 0.297,
and the value of f.sub.2 /f.sub.3 in Cond. (9) is -0.312.
Set out below are the numerical data about Examples 1 to 9.
EXAMPLE 1
______________________________________ Surface Radius of Surface
Refractive No. curvature separation index Abbe's No.
______________________________________ 1 (pupil position E) 17.785
2 -104.0275 18.000 1.4870 70.4 3 -92.3647 16.000 1.4880 69.7 4
-69.1938 -16.000 1.4880 69.7 (reflective surface 122) 5 -92.3647
16.000 1.4880 69.7 (reflective surface 121) 6 -69.1938 16.308 7
(image plane I) ______________________________________
EXAMPLE 2
______________________________________ Surface Radius of Surface
Refractive No. curvature separation index Abbe's No.
______________________________________ 1 (pupil position E) 16.543
2 -422.9719 18.000 1.4870 70.4 3 -89.7455 22.939 1.4870 70.4 4
-76.5015 -22.939 1.4870 70.4 (reflective surface 122) 5 -89.7455
22.939 1.4870 70.4 (reflective surface 121) 6 -76.5015 2.000 7
(image plane I) ______________________________________
EXAMPLE 3
______________________________________ Surface Radius of Surface
Refractive No. curvature separation index Abbe's No.
______________________________________ 1 (pupil position E) 12.588
2 -329.5184 18.000 1.4870 70.4 3 -105.1892 28.327 1.7550 27.6 4
-87.3558 -28.327 1.7550 27.6 (reflective surface 122) 5 -105.1892
28.327 1.7550 27.6 (reflective surface 121) 6 -87.3558 2.000 7
(image plane I) ______________________________________
EXAMPLE 4
______________________________________ Surface Radius of Surface
Refractive No. curvature separation index Abbe's No.
______________________________________ 1 (pupil position E) 10.060
2 -248.9365 18.000 1.4870 70.4 3 -129.2398 5.000 4 -77.9293 27.814
1.7550 27.6 5 -76.6712 -27.814 1.7550 27.6 (reflective surface 122)
6 -77.9293 27.814 1.7550 27.6 (reflective surface 121) 7 -76.6712
2.000 8 (image plane I) ______________________________________
EXAMPLE 5
______________________________________ Surface Radius of Surface
Refractive No. curvature separation index Abbe's No.
______________________________________ 1 (pupil position E) 38.768
2 -41.8658 18.543 1.7550 27.6 3 -50.4784 -18.543 1.7550 27.6
(reflective surface 122) 4 -41.8658 18.543 1.7550 27.6 (reflective
surface 121) 5 -50.4784 7.524 1.4870 70.5 6 -57.9049 6.029 7 (image
plane I) ______________________________________
EXAMPLE 6
______________________________________ Surface Radius of Surface
Refractive No. curvature separation index Abbe's No.
______________________________________ 1 (pupil position E) 28.053
2 -53.8255 18.051 1.5421 53.2 3 -55.3799 -18.051 1.5421 53.2
(reflective surface 122) 4 -53.8255 18.051 1.5421 53.2 (reflective
surface 121) 5 -55.3799 0.100 6 -93.2945 6.473 1.4870 70.4 7
-80.7336 5.130 8 (image plane I)
______________________________________
EXAMPLE 7
______________________________________ Surface Radius of Surface
Refractive No. curvature separation index Abbe's No.
______________________________________ 1 (pupil position E) 17.875
2 405.1484 34.590 1.4870 70.4 3 -63.3309 18.359 1.7550 27.6 4
-65.2942 -18.359 1.7550 27.6 (reflective surface 122) 5 -63.3309
18.359 1.7550 27.6 (reflective surface 121) 6 -65.2942 4.000 1.7550
27.6 7 -4740.8773 6.038 8 (image plane I)
______________________________________
EXAMPLE 8
______________________________________ Surface Radius of Surface
Refractive No. curvature separation index Abbe's No.
______________________________________ 1 (pupil position E) 40.267
2 490.3546 8.513 1.4870 70.4 3 -140.5902 22.000 1.5329 52.8 4
-87.0972 -22.000 1.5329 52.8 (reflective surface 122) 5 -140.5902
22.000 1.5329 52.8 (reflective surface 121) 6 -87.0972 5.000 1.7550
27.6 7 -96.4051 2.000 8 (image plane I)
______________________________________
EXAMPLE 9
______________________________________ Surface Radius of Surface
Refractive No. curvature separation index Abbe's No.
______________________________________ 1 (pupil position E) 21.690
2 722.9395 22.931 1.4870 71.2 3 -86.1417 2.328 4 -76.5282 22.042
1.7550 27.6 5 -73.5076 -22.042 1.7550 27.6 (reflective surface 122)
6 -76.5282 22.042 1.7550 27.6 (reflective surface 121) 7 -73.5076
0.742 8 -74.4603 5.000 1.7550 27.6 9 -218.7444 2.000 10 (image
plane I) ______________________________________
Referring to Examples 1-9 as above mentioned, now let f.sub.1
denote the focal length of lens 11, f.sub.2 the focal length of
concentric system 12, f.sub.3 the focal length of lens 13, R.sub.01
the radius of curvature of the surface of lens 11 proximate to the
pupil plane E, R.sub.02 the radius of curvature of the surface of
lens 11 proximate to the image plane I, R.sub.11 the radius of
curvature of the surface of lens 13 proximate to the pupil plane E,
R.sub.12 the radius of curvature of the surface of lens 13
proximate to the image plane I, and R.sub.3 the radius of curvature
of the surface of concentric system 12 proximate to the image plane
I. Set out in Tables 1 and 2 are the values of f.sub.1, 1/R.sub.01,
1/R.sub.02, 1/R.sub.3, 1/R.sub.11, 1/R.sub.12, f.sub.2, f.sub.3,
f.sub.2 /f.sub.1, and f.sub.2 /f.sub.3.
TABLE 1 ______________________________________ f.sub.1 1/R.sub.01
1/R.sub.02 1/R.sub.3 1/R.sub.11
______________________________________ Ex. 1 1123.71 -0.0096
-0.0108 -0.0145 2 296.74 -0.0029 -0.0096 -0.0115 3 309.15 -0.0030
-0.0095 -0.0114 4 526.01 -0.0040 -0.0077 -0.0130 5 -0.0198 -0.0198
6 -0.0181 -0.0107 7 115.25 0.0025 -0.0158 -0.0153 -0.0153 8 225.36
0.0020 -0.0071 -0.0115 -0.0115 9 159.53 0.0014 -0.0116 -0.0136
-0.0134 ______________________________________
TABLE 2 ______________________________________ 1/R.sub.12 f.sub.2
f.sub.3 f.sub.2 /f.sub.1 f.sub.2 /f.sub.3
______________________________________ Ex. 1 43.62 0.0388 2 45.23
0.1524 3 45.00 0.1456 4 43.20 0.0821 5 -0.0173 37.96 -1209.60
-0.0314 6 -0.0124 39.30 1053.49 0.0373 7 -0.0002 50.64 -87.72
0.4394 -0.5773 8 -0.0104 44.52 -1553.93 0.1976 -0.0286 9 -0.0046
47.34 -151.78 0.2967 -0.3119
______________________________________
As already mentioned, the optical system according to the present
invention may be used as an ocular or image-forming system. One
example will now be explained. For the image-forming system, it is
possible to use a finder system Fi of a compact camera Ca, which is
substantially juxtaposed to a photographic system Ob, as typically
shown in the perspective view of FIG. 19. Alternatively, an
objective system Lo may be built up of a front lens group GF, an
aperture diaphragm D, and an optical system ML of the present
invention which is located in the rear of the diaphragm D, and is
constructed from a concentric element 12 comprising a first
semitransparent surface 121 and a second semitransparent surface
122 and a dioptric element 13 located in the vicinity thereof, as
shown in the sectional view of FIG. 20. An image formed by this
objective system Lo is erected by a Porro prism P located on the
viewer side of the objective system Lo and designed to cause the
image to be reflected four times, and is then viewed through an
eyepiece Oc.
Furthermore, when the optical system of the present invention is
used as an image-forming system, it may be constructed in the form
of a front aperture system.
In another preferable embodiment, the optical system of the present
invention is used as an ocular system for a head mount type of
image display unit HMD which enables a virtual image to be
magnified and projected in the eyeballs of a viewer, so that the
viewer can view a virtually magnified image. This ocular system, as
typically shown in the sectional view of FIG. 21(b), is built up of
a liquid crystal display device LCD for displaying an image, and an
optical system ML of the present invention made up of a concentric
element 12 comprising a first semitransparent surface 121 and a
second semitransparent surface 122 and a dioptric element 11
located in the vicinity thereof, so that the image displayed on the
LCD can be magnified and projected in the eyeballs of the viewer.
When the dioptric element 13 is positioned on the LCD side of the
concentric element 12, the concentric and dioptric elements 12 and
13 correspond to first and second prisms, respectively, while the
curved surface 121 of the concentric element 12 located on the
pupil plane side E, the LCD-side curved surface 122 of the
concentric element 12 and the LCD-side curved surface 132 of the
dioptric element 13 correspond to first, second and third surfaces,
respectively, as can be seen from the sectional view of FIG. 21(b).
The light from the display device LCD is refracted and reflected at
the respective surfaces, as illustrated.
As can be understood from the foregoing, the present invention can
provide an optical system which is well corrected in terms of both
curvature of field and coma at a field angle of about 120.degree.
and a pupil diameter of about 15 mm and may be applied to both
image pickup and ocular systems. By applying this to an ocular
system, it is possible to achieve a compact head mount type of
image display unit which enables even a peripheral field angle
region to be clearly viewed at a given wide field angle.
* * * * *